写入操作后数据未出现在日志文件中

Question

我有以下代码：

time = os.date("*t")
data = io.open("test.txt", "a")

function applicationWatcher(appName, eventType, appObject)
    if (eventType == hs.application.watcher.launched) then
        data:write("" .. appName .. " launched at ".. ("%02d:%02d:%02d:%02d:%02d:%02d"):format(time.day, time.month, time.year, time.hour, time.min, time.sec))
    end
end

local appWatcher = hs.application.watcher.new(applicationWatcher)
appWatcher:start()

当您在 macOS 上启动应用程序时会看到此代码。我希望程序将时间、日期和应用程序的名称记录在一个文件中，以便我可以查看我启动了哪些应用程序以及启动时间。

似乎没有任何内容登录到我的文本文件中。为什么？

Answer 1

文件 I/O 是 buffered。这意味着数据并不总是立即写入文件，而是保存在内存中直到缓冲区已满，这样数据就可以批量写入。

简单的解决方法是简单地使用 file:flush 立即将缓冲区中的数据推送到文件中。

data:write('name and timestamp')
data:flush()

更高级的解决方案是使用file:setvbuf设置你合适的mode，并缓冲size:

file:setvbuf (mode [, size])

Sets the buffering mode for an output file. There are three available modes:

"no": no buffering; the result of any output operation appears immediately.

"full": full buffering; output operation is performed only when the buffer is full or when you explicitly flush the file (see io.flush).

"line": line buffering; output is buffered until a newline is output or there is any input from some special files (such as a terminal device).

For the last two cases, size specifies the size of the buffer, in bytes. The default is an appropriate size.

你可能想要的是 'line' 缓冲，因为无论如何你都应该在字符串的末尾添加一个换行符 ('\n')，否则你的日志文件将很难阅读.

local data = io.open("test.txt", "a")
data:setvbuf('line')

写入操作后数据未出现在日志文件中

Data not appearing in log file after write operation

file

lua

hammerspoon

`file:setvbuf (mode [, size])`